American Coco Gauff defeated world number one Aryna Sabalenka 7-6(4), 6-3 in the semi-finals of the WTA Finals on Friday and will take on China's Zheng Qinwen in the showpiece match.
Sabalenka will end the year at the top of the world rankings but her bid for a maiden WTA Finals title was ended by Gauff who reached her first final at the end-of-season event.
Earlier, seventh seed Zheng overcame battling Czech Barbora Krejcikova 6-3, 7-5 to reach Saturday's showpiece on her debut.
It had promised to be a close affair between Sabalenka and world number three Gauff, with the head-to-head record standing at 4-4, and the opening set lived up to expectations.
After trading early breaks, Sabalenka broke again to take a 6-5 lead to serve for the set but Gauff responded, forcing a tiebreak which saw eight breaks of serve over the 11 points.
The American cruised to a 6-1 lead, breaking Sabalenka four times, before the Belarusian broke twice to save the first two set points but Gauff held her nerve to win the first set.
Sabalenka cut a frustrated figure throughout the match and Gauff raced into a 4-1 lead in the second set before the sixth game turned into a marathon affair.
Gauff saved seven break points and at one stage Sabalenka threw her racket into the air but eventually won the game to keep the contest alive. However, the American then broke to love to serve for the match.
Sabalenka rallied and broke again but Gauff kept her cool and, just when it seemed Sabalenka would claw her way back into the tie, the American broke for a fourth time in the second set.
"I'm happy with the way I played, she's world number one for a reason," said Gauff, who can now look forward to Saturday's final against Zheng.
"I'm not really nervous to be honest and the year-end I see it as just a plus and being here is a reward for the season I've had," the third seed added.
China's Olympic gold medallist Zheng, making her WTA Finals debut, got off to a great start against eighth seed Krejcikova, with an early break to take a 3-0 lead.
The Czech saved three set points at 5-2 down but Zheng won the next game to love and took the first set with ease.
The second set looked to be going the same way as Zheng again raced into a 3-0 lead, this time with two breaks of serve, but Krejcikova finally got into her groove, winning the next four games with two breaks of her own.
The next three games went with serve to leave the pair tied at 5-5 before Zheng managed to break again, leaving her to serve for the match. Krejcikova fought hard, saving the first match point, but Zheng finally got the job done.
"It feels so special. This is my first WTA Finals, and now I'm in the final," Zheng said. "She (Krejcikova) is a really good player. We gave a good match. I don't know what happened when I was leading 3-0."
